If you save the beneficiary IBAN (the account you are paying into) as a trusted account, you will remove the requirement of authorising payments via the CaixaBank Sign app.
Go into your CaixaBank online banking, select 'Transferencias' and ‘Gestionar cuentas de confianza. Then add the IBAN of the bank you are paying into.
This has huge benefits if regularly paying into the same account.