Redirect to https... all pages but one - apache

Question

i am having an issue
I have a website that i must always redirect to https... EXCEPT ONE PAGE because i am using ATOS SIPS and it doesnt accept ssl.
So my page i have not to rewirte is this :
example.com/paiement-debiteurs?task=retour
with only THIS parameter.
My htaccess does this :
RewriteEngine On
RewriteCond %{SERVER_PORT} 80
RewriteRule ^(.*)$ https://example.com/$1 [R=301,L]
And before that i tried many things
The best i ever got to work is this , put before:
RewriteCond %{QUERY_STRING} (^|.*&)task=retour(&.*|$)
RewriteRule ^paiement-debiteurs$ - [L]
If i replace that - with any page, it works well and redirect me to that page. But if i leave that dash, it goes to a 404 (and stills redirect me to https!)
I've searched a lot and didnt understood how just to tell apache "You see that page? if its http dont redirect it to https. This page and only this page!"
Can you help me?
Thanks
Edit : there is my whole htaccess
:
## Mod_rewrite
RewriteEngine On
RewriteBase /
## Begin - Rewrite rules to block out some common exploits.
RewriteCond %{QUERY_STRING} base64_encode[^(]*\([^)]*\) [OR]
RewriteCond %{QUERY_STRING} (<|%3C)([^s]*s)+cript.*(>|%3E) [NC,OR]
RewriteCond %{QUERY_STRING} GLOBALS(=|\[|\%[0-9A-Z]{0,2}) [OR]
RewriteCond %{QUERY_STRING} _REQUEST(=|\[|\%[0-9A-Z]{0,2})
RewriteRule .* index.php [F]
RewriteEngine On
RewriteCond %{QUERY_STRING} (^|.*&)task=retour(&.*|$)
RewriteRule ^paiement-debiteurs$ - [L]
RewriteEngine On
RewriteCond %{SERVER_PORT} 80
RewriteRule ^(.*)$ https://example.com/$1 [R=301,L]
## Begin - Joomla! core SEF Section.
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
RewriteCond %{REQUEST_URI} !^/index\.php
RewriteCond %{REQUEST_URI} /component/|(/[^.]*|\.(php|html?|feed|pdf|vcf|raw))$ [NC]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule .* index.php [L]
AddHandler x-mapp-php6 .php
Removing the line RewriteRule ^(.*)$ https://example.com/$1 [R=301,L] removes the https redirection