Where it lives
On a TIE card the support number opens with the letter E followed by a run of digits, for instance E01234567, printed on the front or the reverse of the card.
On a green EU certificate it appears as the IXESP or C-reference; on the older A4 versions you may see it labelled "Nº de soporte" near the top of the sheet.
Why you keep being asked for it
It is the key that lets digital services confirm you really are you — on Cl@ve, the immigration portal and a host of regional sites. Without it, those online procedures simply will not move forward, which is why having it to hand saves a lot of bother.
In Alicante
In Alicante, the número de soporte is handled through Oficina de Extranjería de Alicante; our local team prepares your file and books the cita previa so it clears first time. We help clients from Benidorm to San Juan de Alicante.