All authors have to preregister to the conference (preregistration is not a compromise to attend the conference). This is only the procedure of handling authors data. If you preregistered for some of past ISIPTA conferences, it is not necessary to do it again this year.
When introducing authors and author for correspondence use only authors emails (identical to the one used in preregistration). Use simple spaces as separators. For example: gregor@ero.eef.edu kaled@emus.eaf.es
In case of doubt or if you want to know about your preregistration data, please send an e-mail to smc@decsai.ugr.es (Serafin Moral).