diff --git a/src/offer/dto/offer.dto.ts b/src/offer/dto/offer.dto.ts
index 60b5de4..70bbf7e 100644
--- a/src/offer/dto/offer.dto.ts
+++ b/src/offer/dto/offer.dto.ts
@@ -1,5 +1,5 @@
 import { ApiProperty } from '@nestjs/swagger';
-import { IsNumber, IsString } from 'class-validator';
+import { IsNumber, IsPositive, IsString } from 'class-validator';
 export class OfferDto {
   @ApiProperty({
     type: String,
@@ -16,5 +16,6 @@ export class OfferDto {
     example: 21,
   })
   @IsNumber()
+  @IsPositive()
   amount: number;
 }
diff --git a/src/offer/offer.service.ts b/src/offer/offer.service.ts
index 01af708..ca906d2 100644
--- a/src/offer/offer.service.ts
+++ b/src/offer/offer.service.ts
@@ -43,8 +43,17 @@ export class OfferService {
       },
     });
 
+    const crypto = await this.prisma.crypto.findUnique({
+      where: {
+        id: dto.id_crypto,
+      },
+    });
+    if (!crypto || !crypto.id) {
+      throw new ForbiddenException('Crypto doesnt exist');
+    }
+
     if (!offer || offer.id !== offerId)
-      throw new ForbiddenException('Access to resources denied');
+      throw new ForbiddenException('Offer id mandatory');
 
     return this.prisma.role.update({
       where: {