Thanks for the answers.
I just looked at the "use api explorer" page and saw the note that only stringified JSON can be used with the API explorer.
ALSO, i just found my problem: me
The API Explorer requires stringified JSON because the word "filter" is the parameter:
myRestApi.com?filter={where: {{property:value}}
Whereas, when using the REST syntax, the filter + the query is the parameter:
myRestApi.com?filter[where][title]=test
(note the equals sign is not after the word "filter" in the 2nd example, but between the property and the value.
Learned something new today!