This webpage assigns consecutive participant numbers and then redirected to alternating URLS
Usage: If your survey URLs are https://surveyhero.com/c/c123456 and https://surveyhero.com/c/c7891011 then use https://moryscarter.com/vespr/survey.php?domain=surveyhero.com&folder=c&id1=c123456&id2=c7891011. Only the domain and folder is saved on this site. If your link doesn't have a folder then put "&folder=.". However, this does mean that all links with the same domain will share the same set of participant numbers.
Usage: If your survey URLs are https://run.pavlovia.org/Wake/brookes-template-2020/html/?group=1 and https://run.pavlovia.org/Wake/brookes-template-2020/html/?group=2 then use https://moryscarter.com/vespr/survey.php?domain=run.pavlovia.org&folder=Wake/brookes-template-2020/html/&vars=group&id1=A&id2=B&id3=C. Only the domain and folder is saved on this site.
N.B. You can use a maximum of six options id1-id6
Reference (APA 7th): Morys-Carter, W.L. (2021, April 19). Alternating allocation to surveys. VESPR. https://moryscarter.com/vespr/survey.php.