diff --git a/servers/mu/src/domain/clients/relay.test.js b/servers/mu/src/domain/clients/relay.test.js
index 20512f2ed..9ca9c8b0e 100644
--- a/servers/mu/src/domain/clients/relay.test.js
+++ b/servers/mu/src/domain/clients/relay.test.js
@@ -32,7 +32,7 @@ describe('topUpWith function', function () {
   logger.tap = () => (args) => {
     return args
   }
-  const fetchTransactionDetails = async () => {
+  const fetchTransactions = async () => {
     return {
       data: {
         transactions: {
@@ -49,7 +49,7 @@ describe('topUpWith function', function () {
       }
     }
   }
-  let topUp = topUpWith({ fetch, logger, wallet, address, fetchTransactionDetails })
+  let topUp = topUpWith({ fetch, logger, wallet, address, fetchTransactions })
 
   it('should correctly sign and verify a request', async function () {
     const params = {
diff --git a/servers/mu/src/domain/lib/write-message-tx.js b/servers/mu/src/domain/lib/write-message-tx.js
index ed1f4325b..b2c08a6e5 100644
--- a/servers/mu/src/domain/lib/write-message-tx.js
+++ b/servers/mu/src/domain/lib/write-message-tx.js
@@ -43,6 +43,16 @@ export function writeMessageTxWith (env) {
             if(!amount || !sender) {
               return Rejected(new Error('Must set Sender and Quantity to top up.', { cause: ctx }))
             }
+
+            if(!Object.keys(RELAY_MAP).includes("ALLOWED_CURRENCIES")) {
+              return Rejected(new Error('No allowed currencies configured on this MU.', { cause: ctx }))
+            }
+
+            if(!RELAY_MAP["ALLOWED_CURRENCIES"].includes("ALL")) {
+              if(!RELAY_MAP["ALLOWED_CURRENCIES"].includes(ctx.cachedMsg.fromProcessId)) {
+                return Rejected(new Error('This currency is not supported on this MU.', { cause: ctx }))
+              }
+            }
             
             return topUp({ctx, relayUrl: RELAY_MAP[ctx.tx.processId].url, amount, recipientProcessId: sender})
               .bimap(
diff --git a/servers/mu/src/domain/lib/write-message-tx.test.js b/servers/mu/src/domain/lib/write-message-tx.test.js
index 3480e144f..55dbfc83a 100644
--- a/servers/mu/src/domain/lib/write-message-tx.test.js
+++ b/servers/mu/src/domain/lib/write-message-tx.test.js
@@ -96,6 +96,7 @@ describe('writeMessageTxWith', () => {
         }
       },
       RELAY_MAP: {
+        'ALLOWED_CURRENCIES': ["fromid"],
         'mappedid1': { 'url': 'url1' },
         'mappedid2': { 'url': 'url1' }
       },
@@ -115,6 +116,7 @@ describe('writeMessageTxWith', () => {
         url: 'https://foo.bar'
       },
       cachedMsg: {
+        fromProcessId: 'fromid',
         msg: {
           Tags: [{
             name: 'Action',
@@ -156,6 +158,7 @@ describe('writeMessageTxWith', () => {
         }
       },
       RELAY_MAP: {
+        'ALLOWED_CURRENCIES': ["ALL"],
         'mappedid1': { 'url': 'url1' },
         'mappedid2': { 'url': 'url1' }
       },