ODK access problems / problemas acceso ODK

At the time of submitting the form, the certificate error message appears. the security certificate was bought, but the error is still coming out.

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Al momento de enviar formulario sale el mensaje de error de certificado. el certificado de seguridad se compro, pero todavía sigue saliendo el error.

What server URL is this form being submitted to?

https://odk.cruzrojacolombiana.org:8443/MIGRACION/

ODK Aggregate is no longer being updated. We recommend you use ODK Central.

As to the problem at hand, my guess is that you are using a very old phone and that phone doesn't have the root certificates that would enable it to trust the server. What version of Android are you running?