Error shows, installation of payment process

I need a help from somebody, we are trying to install the payment process with a supplier Sr Pago in my REGION in Mexico, but unfortunately, we cannot continue with this installation because in the test process, we made some test in the Sandbox escenario but, at the moment to conclude the payment in the application, it send a message with the single word, ERROR. I received an email from my supplier who said that this error is caused by the next portion of code, then I need some help in order to conclude this installation of the payment process

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