As per Table 210 "Additional entries specific to a URI action" of ISO 32000-2:2020, the URI entry should be set to the full URL of this webpage and the IsMap entry should be set to true.
<< /Type /Annot /Subtype /Link /Rect [0 0 720 523] /A << /S /URI /URI (https://safedocs.pdfa.org/uri-ismap-test.html) /IsMap true >> ... >>
The location of each click will then get shown on this image (720 x 523 pixels) by processing received URLs of the form "https://safedocs.pdfa.org/uri-ismap-test.html?100,200":
X = x, Y = y