It seems to me that the Parsoid API does not work properly for ba.wikibooks.org.
Example:
1 - https://ba.wikibooks.org/wiki/%D0%92%D0%B8%D0%BA%D0%B8%D0%B4%D3%99%D1%80%D0%B5%D1%81%D0%BB%D0%B5%D0%BA:%D0%91%D0%B0%D1%88_%D0%B1%D0%B8%D1%82 is the welcome page of ba.wikibooks.org and works fine
2 - but https://ba.wikibooks.org/api/rest_v1/page/html/%D0%92%D0%B8%D0%BA%D0%B8%D0%B4%D3%99%D1%80%D0%B5%D1%81%D0%BB%D0%B5%D0%BA:%D0%91%D0%B0%D1%88_%D0%B1%D0%B8%D1%82 gives me the following JSON
{"type":"https://mediawiki.org/wiki/HyperSwitch/errors/not_found#route","title":"Not found.","method":"get","uri":"/ba.wikibooks.org/v1/page/html/%D0%92%D0%B8%D0%BA%D0%B8%D0%B4%D3%99%D1%80%D0%B5%D1%81%D0%BB%D0%B5%D0%BA%3A%D0%91%D0%B0%D1%88_%D0%B1%D0%B8%D1%82"}
instead of the page HTML.