snakemake: AmbiguousRuleException

pairs = {"P1" : "P1", "P2" : "P2"}
samples = {
    "sample1": "sample1",
    "sample2": "sample2"
}
wildcard_constraints:
    pair = "|".join(pairs),
    sample = "|".join(samples),
rule all:
    input: expand("data/{sample}/{sample}_concatenated.txt", sample = samples)
rule get_txt_files:
    output:
        "data/{sample}_{pair}.txt"
    shell:
        """
        echo 1 > {output}
        """
rule reorganise:
  input:
    expand("data/{{sample}}_{pair}.txt", \
        pair=pairs)
  output:
    "data/{sample}/{sample}_{pair}.txt"
  shell:
    "mv {input} data/{wildcards.sample}/."
rule concat:
    input:
        expand("data/{{sample}}/{{sample}}_{pair}.txt", \
            pair=pairs)
    output:
        "data/{sample}/{sample}_concatenated.txt"
    shell:
        "cat {input} > {output}"