diff --git a/pyproject.toml b/pyproject.toml
index bdb80889..327ef826 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -13,6 +13,7 @@ dependencies = [
     "python-json-logger>=2.0.0",
     "cashu",
     "secp256k1",
+    "marshmallow>=3.13,<4.0",
 ]
 
 [dependency-groups]
diff --git a/uv.lock b/uv.lock
index a0cb0783..b1fb8dc5 100644
--- a/uv.lock
+++ b/uv.lock
@@ -957,11 +957,14 @@ wheels = [
 
 [[package]]
 name = "marshmallow"
-version = "4.0.0"
+version = "3.26.1"
 source = { registry = "https://pypi.org/simple" }
-sdist = { url = "https://files.pythonhosted.org/packages/1e/ff/26df5a9f5ac57ccf693a5854916ab47243039d2aa9e0fe5f5a0331e7b74b/marshmallow-4.0.0.tar.gz", hash = "sha256:3b6e80aac299a7935cfb97ed01d1854fb90b5079430969af92118ea1b12a8d55", size = 220507 }
+dependencies = [
+    { name = "packaging" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/ab/5e/5e53d26b42ab75491cda89b871dab9e97c840bf12c63ec58a1919710cd06/marshmallow-3.26.1.tar.gz", hash = "sha256:e6d8affb6cb61d39d26402096dc0aee12d5a26d490a121f118d2e81dc0719dc6", size = 221825 }
 wheels = [
-    { url = "https://files.pythonhosted.org/packages/d6/26/6cc45d156f44dbe1d5696d9e54042e4dcaf7b946c0b86df6a97d29706f32/marshmallow-4.0.0-py3-none-any.whl", hash = "sha256:e7b0528337e9990fd64950f8a6b3a1baabed09ad17a0dfb844d701151f92d203", size = 48420 },
+    { url = "https://files.pythonhosted.org/packages/34/75/51952c7b2d3873b44a0028b1bd26a25078c18f92f256608e8d1dc61b39fd/marshmallow-3.26.1-py3-none-any.whl", hash = "sha256:3350409f20a70a7e4e11a27661187b77cdcaeb20abca41c1454fe33636bea09c", size = 50878 },
 ]
 
 [[package]]
@@ -1328,6 +1331,7 @@ dependencies = [
     { name = "fastapi", extra = ["standard"] },
     { name = "greenlet" },
     { name = "httpx", extra = ["socks"] },
+    { name = "marshmallow" },
     { name = "python-json-logger" },
     { name = "secp256k1" },
     { name = "sqlmodel" },
@@ -1351,6 +1355,7 @@ requires-dist = [
     { name = "fastapi", extras = ["standard"], specifier = ">=0.115" },
     { name = "greenlet", specifier = ">=3.2.1" },
     { name = "httpx", extras = ["socks"], specifier = ">=0.25.2" },
+    { name = "marshmallow", specifier = ">=3.13,<4.0" },
     { name = "python-json-logger", specifier = ">=2.0.0" },
     { name = "secp256k1", git = "https://github.com/saschanaz/secp256k1-py?branch=upgrade060" },
     { name = "sqlmodel", specifier = ">=0.0.24" },