automatically set the value of a custom field based on the value selected on the sales method

We have a requirement to automatically set the value of a custom field based on the value selected in the Sales Method field in oracle cx sales app.

This functionality is working correctly in the Redwood web application. However, the same requirement is not working in the Oracle CX Sales Mobile application.

I have configured the On Field Value Change event with SalesMethodId as the dependent field and used the following script:

if (this.SalesMethodId === '3000000000') {
this.customfield_c = 'ABC';
}
else if (this.SalesMethodId === '3000001') {
this.customfield_c = 'DEF';
}
else if (this.SalesMethodId === '30000002') {
this.customfield_c = 'GHI';