IBAN to SEPA converter

I have a UK bank account, and the IBAN number follows this example format as expected:

GB45 LOYD 6016 1331 9268 19

When I log onto the Spanish utility company Iberdrola, I select the UK from the dropdown box as I want to change my SEPA to another bank based in the UK. However, it is not allowing me to input the LOYD letters, and it expects the ending to be four numbers not two as shown in the format above. As an experiment I tried all of the other countries on the list, and the same formatting problem occurs.

Iberdrola is a massive multinational utility company, so I doubt they could have this glitch on their website for over thirteen years. This leads me to believe that perhaps IBAN is not the same as SEPA.

Question: How can I convert my Starling bank Euro account IBAN into a SEPA complaint format? Otherwise, how can I convert the bank code LOYD into a number?

Irrespective, all UK banks whether they store pounds or Euros seem to have four letters, such as LOYD, which is not allowed as it does not follow the SEPA format.

The example above uses LOYD, but Starling’s bank code is SRLG, it was just an example to help explain the question.