Hello Luis,
the eon_mobile_paymentex object from appeon_workaround.pbl provides you the API.

https://www.appeon.com/support/documents/appeon_online_help/2017/workarounds_and_api_guide/ch01s04s14.html

A short howto:

1) Declare payment object and related structures

eon_mobile_paymentex lnv_payment
eon_mobile_str_paymentinit lstr_paymentinit
eon_mobile_str_paymentsubmit lstr_paymentsubmit

2) Initialize payment record for given provider (e.g. PayPal), for which you need to have a merchant ID

lnv_payment = create eon_mobile_paymentex
istr_paymentinit.s_clientid = "set here PayPal ID for the merchant"
istr_paymentinit.s_clientid = "your client ID"
inv_payment.of_setappplatform(1) // payPal
inv_payment.of_init(istr_paymentinit)

3) register callback events to know when payment is completed/failed

inv_payment.of_register( this, "ue_paymentok","ue_paymentcancel","ue_paymentfailed","ue_error" )

4) Issue payment

lstr_paymentsubmit.dbl_countmoney = 10.00
lstr_paymentsubmit.s_currency = "EUR"
lstr_paymentsubmit.s_productname = "Order from my store"
lnv_payment.of_submit(lstr_paymentsubmit)

Best,
Marco