Thanks for your help @Dumitru,
I finally got the plugin back without paying 
unfortunately, I must be idiot because all my calls end up with an ā{āerrorā:āinvalid_grantā,āerror_descriptionā:āauthentication failureā}ā error. I tried to fix it myself, unsuccessfully.
I went back to your setup tutorial (here) end did this :
- I went back to my previous āconnected appā in Salesforce
- Copied the key and the secret at the right place in the bubble plugin settings.
- changed the callback url (thatās a part I am really confused about, I am supposed to right the url of the pages that use the api right ? before all this I just had āhttp://ā and it worked fine")
if you (or anyone else) understand where have I committed a stupid mistake, please tell me 
Regards,