fix(backend): Set the minimum auto top-up amount to 500 credits (#9418)

### Changes 🏗️

* Set the minimum auto top-up amount to 500.
* Add description on minimum and dollar value in the input box.

### Checklist 📋

#### For code changes:
- [ ] I have clearly listed my changes in the PR description
- [ ] I have made a test plan
- [ ] I have tested my changes according to the test plan:
  <!-- Put your test plan here: -->
  - [ ] ...

<details>
  <summary>Example test plan</summary>
  
  - [ ] Create from scratch and execute an agent with at least 3 blocks
- [ ] Import an agent from file upload, and confirm it executes
correctly
  - [ ] Upload agent to marketplace
- [ ] Import an agent from marketplace and confirm it executes correctly
  - [ ] Edit an agent from monitor, and confirm it executes correctly
</details>

#### For configuration changes:
- [ ] `.env.example` is updated or already compatible with my changes
- [ ] `docker-compose.yml` is updated or already compatible with my
changes
- [ ] I have included a list of my configuration changes in the PR
description (under **Changes**)

<details>
  <summary>Examples of configuration changes</summary>

  - Changing ports
  - Adding new services that need to communicate with each other
  - Secrets or environment variable changes
  - New or infrastructure changes such as databases
</details>

autogpt_platform/backend/backend/server/routers/v1.py

@@ -177,6 +177,8 @@ async def configure_user_auto_top_up(
 ) -> str:
     if request.threshold < 0:
         raise ValueError("Threshold must be greater than 0")
+    if request.amount < 500:
+        raise ValueError("Amount must be greater than or equal to 500")
     if request.amount < request.threshold:
         raise ValueError("Amount must be greater than or equal to threshold")
 

autogpt_platform/frontend/src/app/marketplace/(user)/credits/page.tsx

@@ -108,7 +108,7 @@ export default function CreditsPage() {
                 htmlFor="topUpAmount"
                 className="mb-1 block text-neutral-700"
               >
-                Top-up Amount (Credits)
+                Top-up Amount (Credits, Minimum 500 = 5 USD)
               </label>
               <input
                 type="number"
@@ -137,7 +137,7 @@ export default function CreditsPage() {
                 htmlFor="autoTopUpAmount"
                 className="mb-1 block text-neutral-700"
               >
-                Auto Top-up Amount (Credits)
+                Auto Top-up Amount (Credits, Minimum 500 = 5 USD)
               </label>
               <input
                 type="number"
@@ -145,6 +145,7 @@ export default function CreditsPage() {
                 name="topUpAmount"
                 defaultValue={autoTopUpConfig?.amount || ""}
                 placeholder="Enter auto top-up amount"
+                min="500"
                 step="100"
                 className="w-full rounded-md border border-slate-200 px-4 py-2 dark:border-slate-700 dark:bg-slate-800"
                 required
@@ -164,6 +165,7 @@ export default function CreditsPage() {
                 name="threshold"
                 defaultValue={autoTopUpConfig?.threshold || ""}
                 placeholder="Enter threshold value"
+                min="500"
                 step="100"
                 className="w-full rounded-md border border-slate-200 px-4 py-2 dark:border-slate-700 dark:bg-slate-800"
                 required