the custom code in paginated report in report server not working

Hi, 

I custom a function in my report builder which can get response json from other server and generate a new url for me.  my code is like this:

Function Div_RT(ByVal DR As String) As String
Dim request_bbox As System.Net.HttpWebRequest
Dim response_bbox As System.Net.HttpWebResponse = Nothing
Dim reader_bbox As System.IO.StreamReader
Dim DR2 as String = Replace(DR, ",","_")
Dim getbbox_url as String
getbbox_url ="http://XXXXXXXXXXXXXXX"
request_bbox = DirectCast(request_bbox.Create(getbbox_url), System.Net.HttpWebRequest)
response_bbox = DirectCast(request_bbox.GetResponse(), System.Net.HttpWebResponse)
reader_bbox = New System.IO.StreamReader(response_bbox.GetResponseStream())
Dim rawresp As String
rawresp = reader_bbox.ReadToEnd()

Dim s As String
s = Mid(rawresp, InStr(rawresp, "map_get_extent_linkids")+25, InStr(rawresp, "}}]")-InStr(rawresp, "map_get_extent_linkids")-26)

Dim divrt as String
divrt ="http://XXXXXXXXXXXXXXXXXXXXXXXX"
Div_RT=divrt
End Function

I test this function in my local which can work well( cuz I change the "RSPreviewPolicy" file under C:\Program Files (x86)\Microsoft Report Builder. I update PermissionSetName="FullTrust" instead if "Execution"

<CodeGroup
class="UnionCodeGroup"
version="1"
PermissionSetName="FullTrust"
Name="Report_Expressions_Default_Permissions"
Description="This code group grants default permissions for code in report expressions and Code element. ">
<IMembershipCondition
class="StrongNameMembershipCondition"
version="1"
PublicKeyBlob="0024000004800000940000000602000000240000525341310004000001000100512C8E872E28569E733BCB123794DAB55111A0570B3B3D4DE3794153DEA5EFB7C3FEA9F2D8236CFF320C4FD0EAD5F677880BF6C181F296C751C5F6E65B04D3834C02F792FEE0FE452915D44AFE74A0C27E0D8E4B8D04EC52A8E281E01FF47E7D694E6C7275A09AFCBFD8CC82705A06B20FD6EF61EBBA6873E29C8C0F2CAEDDA2"
/>
</CodeGroup>

then I publish this report to power bi report server, the function cannot work again. so I update the "rssrvpolicy" file under C:\Program Files\Microsoft Power BI Report Server\PBIRS\ReportServer. I update PermissionSetName="FullTrust" instead if "Execution"

<CodeGroup class="UnionCodeGroup" version="1" PermissionSetName="FullTrust" Name="Report_Expressions_Default_Permissions" Description="This code group grants default permissions for code in report expressions and Code element. ">
<IMembershipCondition class="StrongNameMembershipCondition" version="1" PublicKeyBlob="0024000004800000940000000602000000240000525341310004000001000100512C8E872E28569E733BCB123794DAB55111A0570B3B3D4DE3794153DEA5EFB7C3FEA9F2D8236CFF320C4FD0EAD5F677880BF6C181F296C751C5F6E65B04D3834C02F792FEE0FE452915D44AFE74A0C27E0D8E4B8D04EC52A8E281E01FF47E7D694E6C7275A09AFCBFD8CC82705A06B20FD6EF61EBBA6873E29C8C0F2CAEDDA2" />
</CodeGroup>

but it does not work in power bi report server. I also restart the server. can you help to check how can I make this function work?@

v-janeyg-msft