The Mishna in Kesubos 63a says:
A woman who rebels against her husband, [by withholding conjugal
rights from his wife] is fined; her marriage contract is reduced by
seven dinars each week... if a man rebels against his wife, he is
fined and an extra three dinars a week are added to her marriage
contract. Rabbi Yehuda says: Three terapa’ikin...
The Gemara (64a-b)asks: What is different when she is the one
rebelling against him, that we give him compensation for Shabbat, as
her marriage contract is reduced by seven dinars a week, which is one
dinar per day including Shabbat, and what is different for her that we
do not give her compensation for Shabbat but rather only for six days?
The Gemara explains: When it is she who is fined and her marriage
contract is reduced, it does not appear to be Shabbat wages, money
paid for services rendered on Shabbat, [since she doesn't actually pay
anything, she is fined by the reduction of her marriage contract],
Whereas when it is he who is fined and compelled to add additional
money every day to her marriage contract, (64b) מיחזי כשכר שבת it
does appear to be Shabbat wages. Consequently, the Sages decreed that
he should not give her money for Shabbat.
We see from this that although the payment he is giving her is for her NOT receiving her rights, it is still called schar Shabbos, wages of Shabbos.
From here we can learn that it is forbidden to receive payment for NOT doing something on Shabbos.
[heard from Rabbi Yehudah Konner, Rav, Dayan, and posek]