Hi Rodolphe,
I hope you have set all the Parameters perfectly while testing IPN Simulator. There are several important parameters as follows with its expected value
IPN handler URL=https://www.i-mdriver.fr/index.php?option=com_taxibooking&controller=pluginresponse&task=pluginnotification&tmpl=component
payment_status = Complete
business=PAYPAL Merchant Email set in Taxibooking Paypal Method
receiver_email=PAYPAL Merchant Email set in Taxibooking Paypal Method
mc_currency=Order Operating Currency
mc_gross=Order amount
invoice=Order number/Reference Number
Show all fields should be set to YES
We have enabled PayPal debug in your site and from now paypal response will be written in a text file so that we can debug the response returned from PayPal. Please try again and lets check together.
About Thanks page, system could not detect the appropriate Menu Itemid for the thanks page and it was showing default/home menu itemid which is 101. You have 2 languages French and English (French is the default language though), so this should be considered as Multilingual site, but you did not enable few System plugins (Language Filter) which is necessary in a multilingual site. We have enabled System - Language Filter plugin and added a content language (French) here https://www.i-mdriver.fr/administrator/index.php?option=com_languages&view=languages. Now, perfect thanks page is showing. We have submitted few test orders for debugging and also removed those.
Hope this helps.
Thanks a lot