Rerouting and rewriting URL with ARR Application request Routing IIS - url

Question

The setup is the following :
i have 2 websites : one public and one private for our internal ERP. By using the same domaine name :
lesterrassesdadrien.fr.
When using the ARR it allow me to have the following : when someone ask for "lesterrassesdadrien.fr" the router will redirect the demand to the public website which is a wordpress, if the demand ask for "lesterrassesdadrien.fr/erp" it will redirect towards our erp website which is in PHP. here is the code inside the file applicationHost.config for the server in IIS:
<rewrite>
<globalRules>
<clear />
<rule name="lesterrassesdadrien_erp" patternSyntax="Wildcard" stopProcessing="true">
<match url="erp/*" />
<conditions>
<add input="{HTTP_HOST}" pattern="lesterrassesdadrien.fr" />
</conditions>
<action type="Rewrite" url="http://lesterrassesdadrien_erp/{R:1}" />
</rule>
<rule name="lesterrassesdadrien_public" enabled="true" patternSyntax="Wildcard" stopProcessing="true">
<match url="*" />
<conditions>
<add input="{HTTP_HOST}" pattern="lesterrassesdadrien.fr" />
<add input="{SERVER_PORT}" pattern="5000" negate="true" />
<add input="{SERVER_PORT}" pattern="5001" negate="true" />
</conditions>
<action type="Rewrite" url="http://lesterrassesdadrien_public/{R:1}" />
</rule>
</globalRules>
</rewrite>
</system.webServer>
<webFarms>
<webFarm name="lesterrassesdadrien_erp" enabled="true">
<server address="127.0.0.1" enabled="true">
<applicationRequestRouting httpPort="5000" />
</server>
</webFarm>
<webFarm name="lesterrassesdadrien_public" enabled="true">
<server address="127.0.0.1" enabled="true">
<applicationRequestRouting httpPort="5001" />
</server>
</webFarm>
</webFarms>
My problem is that when we click on a link inside the ERP website for exemple :
lesterrassesdadrien.fr/admin/... it will fail and bring me back to the public wordpress website : how to keep or add the "erp/" in front of all link inside my erp website?
My explanation are a bit confusing i believe.
Thanks in advance.
I tried to add this to the rules but with no aval :
<rule name="lesterrassesdadrien_admin" patternSyntax="Wildcard" stopProcessing="true">
<match url="admin/*" />
<conditions>
<add input="{HTTP_HOST}" pattern="lesterrassesdadrien.fr" />
</conditions>
<action type="Rewrite" url="http://lesterrassesdadrien_erp/erp/{R:1}" />
</rule>