HTML4: Insert IBAN by separate fields?

I am not sure with input fields for IBAN numbers. Often the IBAN is separated into different fields.

XX00 0000 0000 0000 0000 00

Sometimes the customers have their IBAN in one line

XX00000000000000000000

If they have the IBAN in one line, they can be tangled by read AND write.

What shall I do?

  • Separate the fields and run the risk of confuse the customers who have the IBAN in one line on their card?
  • Make one input field that allows to make spaces?
  • Additional make an example of a valid IBAN?

EDIT: We have customers who enter from a IBAN: XX00 0000 0000 0000 0000 00 only the first XX00 and getting angry.

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