Integrating ShipStation

[RMApothecary]

I am trying to integrate ShipStation with PrestaShop.

When I follow the ShipStation instructions to modify the .htaccess by adding;

RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization},L]

to the following

<IfModule mod_rewrite.c>
<IfModule mod_env.c>
SetEnv HTTP_MOD_REWRITE On
</IfModule>

RewriteEngine on

#Domain: rachelmoira.me
RewriteRule . - [E=REWRITEBASE:/]
RewriteRule ^api(?:/(.*))?$ %{ENV:REWRITEBASE}webservice/dispatcher.php?url=$1 [QSA,L]
RewriteRule ^upload/.+$ %{ENV:REWRITEBASE}index.php [QSA,L]
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization},L]

Everything on my website "breaks", none of the images or pages work.

If I take out the

RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization},L]

Everything works, but ShipStation can not connect.

Am I putting things in the wrong place? Do I need a module?