Lambda Node.js function Can't Access Aurora MySQL

I have a Node.js (ver 16) app in a Lambda Function and I run it on my local machine fine, however when I run the function on AWS I get the following error:

{
  "errorType": "Error",
  "errorMessage": "ER_ACCESS_DENIED_ERROR: Access denied for user 'mailQueue'@'172.31.40.76' (using password: YES)",
  "trace": [
    "Error: ER_ACCESS_DENIED_ERROR: Access denied for user 'mailQueue'@'172.31.40.76' (using password: YES)",
    "    at Handshake.Sequence._packetToError (/var/task/node_modules/mysql/lib/protocol/sequences/Sequence.js:47:14)",
    "    at Handshake.ErrorPacket (/var/task/node_modules/mysql/lib/protocol/sequences/Handshake.js:123:18)",
    "    at Protocol._parsePacket (/var/task/node_modules/mysql/lib/protocol/Protocol.js:291:23)",
    "    at Parser._parsePacket (/var/task/node_modules/mysql/lib/protocol/Parser.js:433:10)",
    "    at Parser.write (/var/task/node_modules/mysql/lib/protocol/Parser.js:43:10)",
    "    at Protocol.write (/var/task/node_modules/mysql/lib/protocol/Protocol.js:38:16)",
    "    at Socket.<anonymous> (/var/task/node_modules/mysql/lib/Connection.js:88:28)",
    "    at Socket.<anonymous> (/var/task/node_modules/mysql/lib/Connection.js:526:10)",
    "    at Socket.emit (node:events:527:28)",
    "    at Socket.emit (node:domain:475:12)",
    "    --------------------",
    "    at Protocol._enqueue (/var/task/node_modules/mysql/lib/protocol/Protocol.js:144:48)",
    "    at Protocol.handshake (/var/task/node_modules/mysql/lib/protocol/Protocol.js:51:23)",
    "    at PoolConnection.connect (/var/task/node_modules/mysql/lib/Connection.js:116:18)",
    "    at Pool.getConnection (/var/task/node_modules/mysql/lib/Pool.js:48:16)",
    "    at Runtime.exports.handler (/var/task/index.js:15:10)",
    "    at Runtime.handleOnceNonStreaming (file:///var/runtime/index.mjs:1028:29)"
  ]
}

The Aurora Security group allows connections from 172.31.0.0/16 and the reachability analyser gives it the ok.

So it appears to be mySQL having issues. The user appears to have correct permissions from any host.

SHOW GRANTS FOR 'mailQueue'

> GRANT USAGE ON *.* TO `mailQueue`@`%`
> GRANT ALL PRIVILEGES ON `emailTransactions`.* TO `mailQueue`@`%` WITH GRANT OPTION

Any suggestions from anyone?

Confirmed all settings with manuals and searched the net, I'm stumped.