Please find code here :-
For add the payment link into email you need to write the code like below:

<t t-set="base_url" t-value="object.get_base_url()"/>
<a t-attf-href="#{base_url}/payment/pay?reference=#{object.name}&amp;amount=#{object.amount_total}&amp;access_token=#{object.access_token}"> Payment Link </a>

@Jainesh - Thanks, but that's already what I've tried more or less. The problem is object.access_token. That value is different from the access token in the payment link (sales order >> action >> generate payment link)

The access token generated by that action seems to be in the account_move model and not sale_order, thus object.access_token won't work.

Hello, @Great Fermentations,

Hope you are doing well,

When the "Generate Payment Link" button is clicked, a popup (payment_link_wizard) appears.
This popup generates an access token based on sale order data, not the account move.
We are using object.access_token because the wizard uses sale order data, not account move data.

The provided link in the question is missing some parameters between the objects.
Due to these missing parameters, accessing the specific link is not possible

I suggest use the given link to access a specific URL.

I may be wrong about the model, but the access_token value is still different. When I call the object.access_token variable from a sales order email template, it pulls in the value used for the Customer Preview page, not the Payment link page. Quick example here from my environment below. Notice the different values for access_token:

Payment Link: https://<website url>/payment/pay?reference=S00054&amount=94.05&access_token=921190550da5307816d20b643188f8dea5bd0206002acafd1c71abd50c5ffb5a&sale_order_id=54

Customer Preview Link: https://<website url>/my/orders/54?access_token=e7cda3ad-1f32-477e-9bd6-73aa52d530da

My whole reason for going at it this way was to control which payment method is available to the customer. I run two websites with two different payment providers. The default customer preview page shows all the payment providers available, and not the ones associated with a given website. The payment link page gives me the ability to define exactly which one I want to show.