Need help finding a way to update payment account field

I have been told the current Splynx API cannot edit Payment account fields… OK no problem

I have successfully created a custom field and populated it with Splynx API

So every customer has a custom field called ‘stripeid’ with their stripe customer ID string in it.
All I need to do is automatically copy this field to payment account ‘2’ STRIPE , field 1 “Customer Stripe account ID”

This could be a php hook or another way would be to do it inside :StripeCustomerForm.php in the stripe module:

I have tried the following code, but it doesn’t work. No doubt because of incorrect location of :
$this->splynx_user_obj->additional_attributes->stripeid; must be wrong.

I really need just some small help here as I feel I am very close to achieve what I need. I know StripeCustomerForm.php can update Payment account fields so I just need some way to copy my customer field stripeid to field1 of payment account.

Please help if anyone can.