Unable to make a sip call via an ATA 503

Hello everyone,
Please excuse my ignorance as I am new to this.
I have two freepbx boxes. Box 1 is on and box 2 on
In box 1 I creted a custom trunk which dials an extesion.
I created an outbound route to use the trunk.
I have done the above for box 2 but it only works on box 1.I get a busy signal when I configure the ata to point box 2.
The object of this is to enable client one (configured on box 2) to dial a 902xxxxx nuber and connect to client two (configured on box 2)

I hope this makes sense.

Many thanks

You’ve done it wrong. You can find instructions on how to do it properly on page 153 of this document:

Thnaks. The tutorial is informative and will use it to learn more about freepbx.