diff --git a/models/doctype/Payment/Payment.js b/models/doctype/Payment/Payment.js
index 503dd7a2..35cc16fb 100644
--- a/models/doctype/Payment/Payment.js
+++ b/models/doctype/Payment/Payment.js
@@ -38,6 +38,11 @@ export default {
           }
         }
       },
+      formula: (doc) => {
+        if (doc.paymentMethod === 'Cash' && doc.paymentType === 'Pay') {
+          return 'Cash';
+        }
+      },
     },
     {
       fieldname: 'paymentType',
@@ -63,7 +68,7 @@ export default {
         }
       },
       formula: (doc) => {
-        if (doc.paymentMethod === 'Cash') {
+        if (doc.paymentMethod === 'Cash' && doc.paymentType === 'Receive') {
           return 'Cash';
         }
       },
@@ -107,7 +112,7 @@ export default {
         if (value < 0) {
           throw new frappe.errors.ValidationError(
             frappe._(
-              `Payment amount cannot be less than zero. Amount has been reset to max viable amount.`
+              `Payment amount cannot be less than zero. Amount has been reset.`
             )
           );
         }
@@ -121,7 +126,7 @@ export default {
               `Payment amount cannot exceed ${frappe.format(
                 amount,
                 'Currency'
-              )}. Amount has been reset to max viable amount.`
+              )}. Amount has been reset.`
             )
           );
         } else if (value === 0) {
@@ -130,7 +135,7 @@ export default {
               `Payment amount cannot be ${frappe.format(
                 value,
                 'Currency'
-              )}. Amount has been reset to max viable amount.`
+              )}. Amount has been reset.`
             )
           );
         }
@@ -140,6 +145,7 @@ export default {
       fieldname: 'writeoff',
       label: 'Write Off / Refund',
       fieldtype: 'Currency',
+      default: 0,
     },
     {
       fieldname: 'for',
diff --git a/models/doctype/Payment/PaymentServer.js b/models/doctype/Payment/PaymentServer.js
index 7ffe4aaf..55025a91 100644
--- a/models/doctype/Payment/PaymentServer.js
+++ b/models/doctype/Payment/PaymentServer.js
@@ -1,14 +1,91 @@
-import BaseDocument from 'frappejs/model/document';
 import frappe from 'frappejs';
+import BaseDocument from 'frappejs/model/document';
 import LedgerPosting from '../../../accounting/ledgerPosting';
 
 export default class PaymentServer extends BaseDocument {
   async change({ changed }) {
-    if (changed === 'for') {
-      this.amount = 0;
-      for (let paymentReference of this.for) {
-        this.amount += paymentReference.amount;
+    switch (changed) {
+      case 'for': {
+        this.updateAmountOnReferenceUpdate();
+        await this.updateDetailsOnReferenceUpdate();
       }
+      case 'amount': {
+        this.updateReferenceOnAmountUpdate();
+      }
+    }
+  }
+
+  async updateDetailsOnReferenceUpdate() {
+    const { referenceType, referenceName } = this.for[0];
+    if (
+      this.for?.length !== 1 ||
+      this.party ||
+      this.paymentType ||
+      !referenceName ||
+      !referenceType
+    ) {
+      return;
+    }
+
+    const doctype = referenceType;
+    const doc = await frappe.getDoc(doctype, referenceName);
+
+    let party;
+    let paymentType;
+
+    if (doctype === 'SalesInvoice') {
+      party = doc.customer;
+      paymentType = 'Receive';
+    } else if (doctype === 'PurchaseInvoice') {
+      party = doc.supplier;
+      paymentType = 'Pay';
+    }
+
+    this.party = party;
+    this.paymentType = paymentType;
+  }
+
+  updateAmountOnReferenceUpdate() {
+    this.amount = 0;
+    for (let paymentReference of this.for) {
+      this.amount += paymentReference.amount;
+    }
+  }
+
+  updateReferenceOnAmountUpdate() {
+    if (this.for?.length !== 1) return;
+    this.for[0].amount = this.amount;
+  }
+
+  async validate() {
+    this.validateAccounts();
+    this.validateReferenceAmount();
+  }
+
+  validateAccounts() {
+    if (this.paymentAccount !== this.account || !this.account) return;
+    throw new Error(
+      `To Account and From Account can't be the same: ${this.account}`
+    );
+  }
+
+  validateReferenceAmount() {
+    const referenceAmountTotal = this.for
+      .map(({ amount }) => amount)
+      .reduce((a, b) => a + b);
+
+    if (this.amount + (this.writeoff ?? 0) < referenceAmountTotal) {
+      const writeoff = frappe.format(this.writeoff, 'Currency');
+      const payment = frappe.format(this.amount, 'Currency');
+      const refAmount = frappe.format(referenceAmountTotal, 'Currency');
+      const writeoffString =
+        this.writeoff > 0 ? `and writeoff: ${writeoff} ` : '';
+
+      throw new Error(
+        frappe._(
+          `Amount: ${payment} ${writeoffString}is less than the total amount allocated to references: ${refAmount}`
+        )
+      );
     }
   }
 
@@ -55,15 +132,16 @@ export default class PaymentServer extends BaseDocument {
     }
   }
 
-  async afterSubmit() {
-    const entries = await this.getPosting();
-    await entries.post();
-  }
-
   async afterRevert() {
+    this.updateReferenceOutstandingAmount();
     const entries = await this.getPosting();
     await entries.postReverse();
+  }
 
-    // Maybe revert outstanding amount of invoice too?
+  async updateReferenceOutstandingAmount() {
+    await this.for.forEach(async ({ amount, referenceType, referenceName }) => {
+      const refDoc = await frappe.getDoc(referenceType, referenceName);
+      refDoc.update({ outstandingAmount: refDoc.outstandingAmount + amount });
+    });
   }
 }
diff --git a/models/doctype/PaymentFor/PaymentFor.js b/models/doctype/PaymentFor/PaymentFor.js
index 33015b05..fb509e65 100644
--- a/models/doctype/PaymentFor/PaymentFor.js
+++ b/models/doctype/PaymentFor/PaymentFor.js
@@ -4,34 +4,40 @@ export default {
   isSingle: 0,
   isChild: 1,
   keywordFields: [],
-  tableFields: [
-    'referenceType',
-    'referenceName',
-    'amount'
-  ],
+  tableFields: ['referenceType', 'referenceName', 'amount'],
   fields: [
     {
       fieldname: 'referenceType',
       label: 'Reference Type',
-      fieldtype: 'AutoComplete',
+      fieldtype: 'Select',
       options: ['SalesInvoice', 'PurchaseInvoice'],
-      required: 1
+      map: { SalesInvoice: 'Invoice', PurchaseInvoice: 'Bill' },
+      required: 1,
     },
     {
       fieldname: 'referenceName',
       label: 'Reference Name',
       fieldtype: 'DynamicLink',
       references: 'referenceType',
-      required: 1
+      getFilters() {
+        return {
+          outstandingAmount: ['>', 0],
+        };
+      },
+      required: 1,
     },
     {
       fieldname: 'amount',
       label: 'Amount',
       fieldtype: 'Currency',
       formula: (row, doc) => {
-        return doc.getFrom(row.referenceType, row.referenceName, 'outstandingAmount');
+        return doc.getFrom(
+          row.referenceType,
+          row.referenceName,
+          'outstandingAmount'
+        );
       },
-      required: 1
-    }
-  ]
+      required: 1,
+    },
+  ],
 };
diff --git a/src/components/Controls/Select.vue b/src/components/Controls/Select.vue
index 83a341b6..71f75c58 100644
--- a/src/components/Controls/Select.vue
+++ b/src/components/Controls/Select.vue
@@ -4,15 +4,22 @@
       {{ df.label }}
     </div>
     <div
-      class="relative flex items-center justify-end bg-white focus-within:bg-gray-200"
+      class="
+        relative
+        flex
+        items-center
+        justify-end
+        bg-white
+        focus-within:bg-gray-200
+      "
       :class="inputClasses"
     >
       <select
         class="appearance-none bg-transparent focus:outline-none w-full"
         :class="isReadOnly && 'pointer-events-none'"
         :value="value"
-        @change="e => triggerChange(e.target.value)"
-        @focus="e => $emit('focus', e)"
+        @change="(e) => triggerChange(e.target.value)"
+        @focus="(e) => $emit('focus', e)"
       >
         <option
           v-for="option in options"
@@ -52,16 +59,24 @@ import Base from './Base';
 export default {
   name: 'Select',
   extends: Base,
+  methods: {
+    map(v) {
+      if (this.df.map) {
+        return this.df.map[v] ?? v;
+      }
+      return v;
+    },
+  },
   computed: {
     options() {
       let options = this.df.options;
-      return options.map(o => {
+      return options.map((o) => {
         if (typeof o === 'string') {
-          return { label: o, value: o };
+          return { label: this.map(o), value: o };
         }
         return o;
       });
-    }
-  }
+    },
+  },
 };
 </script>