Update docs/topics/merchants/online/sdd/guide-get-mandate.mdx

Co-authored-by: Max B. <17831738+max-koro@users.noreply.github.com>

Author: ntombing

docs/topics/merchants/online/sdd/guide-get-mandate.mdx

@@ -6,7 +6,7 @@ After a SEPA Direct Debit (SDD) B2B mandate has been declared, you may need to r
 You can retrieve a specific mandate using the **payment mandate ID**.
 
 :::tip Prerequisites
-1. **Mandate declaration:** A SEPA Direct Debit mandate must have been previously declared using the `addSepaDirectDebitPaymentMandate` mutation.
+1. **Mandate declaration:** A SEPA Direct Debit mandate must have been previously declared using the [`addSepaDirectDebitPaymentMandate`](./guide-declare) mutation.
 1. **Mandate ID:** You must know the **unique payment mandate ID** of the mandate you want to retrieve.
 :::