How To Fix Paypal Express Error : This transaction is invalid

Recently PayPal has updated its services to require TLS 1.2 for all HTTPS connections, this has caused any Paypal Express payment request that is sent from a non TLS 1.2 protocol will return error msg below :
This transaction is invalid. Please return to the recipient's website to complete your transaction using their regular checkout flow.

If you have such issue, then please follow the solution below.

For v8 site :

1. Apply the TLS 1.2 patch first. (If you have already installed the TLS 1.2 patch before, then please skip to next step).
You can download at : http://www.vpasp.com/sales/addons800.asp and select "TLS 1.2 8.0" to download.
After downloaded, please install it to your v8 site.

2. Open your file paypalproexpress.asp and locate this code (around line 479) :

Shopxmlhttp checkxml_paypalec, x_GatewayLocation, anrequest, resultXML, "POST", xmlerror

3. Please replace to :

dim rheadercnt, rheadertypeary(10), rheadervalueary(10)
rheadercnt = 0
Shopxmlhttp_v8 "auto", x_GatewayLocation, anrequest, resultXML, "POST", xmlerror, rheadercnt, rheadertypeary, rheadervalueary, "",""

4. Save the file and upload to your site.

For v7 site :

1. Apply the TLS 1.2 patch first. (If you have already installed the TLS 1.2 patch before, then please skip to next step).
You can download at : http://www.vpasp.com/sales/addons700.asp and select "TLS 1.2 7.00" to download.
After downloaded, please install it to your v7 site.

2. Open your file paypalproexpress.asp and locate this code (around line 423) :

Shopxmlhttp checkxml_paypalec, x_GatewayLocation, anrequest, resultXML, "POST", xmlerror

3. Please replace to :

dim rheadercnt, rheadertypeary(10), rheadervalueary(10)
rheadercnt = 0
Shopxmlhttp_v8 "auto", x_GatewayLocation, anrequest, resultXML, "POST", xmlerror, rheadercnt, rheadertypeary, rheadervalueary, "",""

4. Save the file and upload to your site.

If you still have issue after applying the above fix, please submit a ticket into our helpdesk at https://helpdesk.vpasp.com.

---